DESCRIPTION The long-term objective of the parent grant is to delineate the role of genetic and environmental factors in human neuropsychiatric disorders through the study of Gilles de la Tourette s syndrome (GTS) and obsessive compulsive disorder (OCD). Recent research has indicated that: (1) there is a greater range of phenotypic expression for GTS (including chronic tics and OCD), (2) GTS, OCD and related disorders are much more common than had previously been thought, and (3) these conditions are hereditary and major genes may affect them. Identifying the genes that affect GTS, OCD and other conditions will be of direct benefit to patients concerned about recurrence in their families. In addition, clarifying the genetics of these disorders may elucidate their pathogenesis. Previous studies suggest that there is an etiologic relationship between GTS and OCD and that a major gene may affect expression of these conditions. However, these studies have been done on families ascertained through clinics, thus this population may not be representative of GTS and OCD families. Based on previous work, only a minority of individuals with GTS seek help for their condition. The proposed study will ascertain families through a large population-based epidemiological survey. These data will allow a more complete characterization of the range of expression of these conditions as well as a more thorough examination of the familial patterns observed. Approximately 100 families of individuals with GTS, chronic tics and/or OCD will be enrolled. The methods of assessment will be identical to those used in the parent grant. In addition, blood samples will be collected so that molecular genetic analyses can be done.